Sweet Shooter, if you mean you're laying a finger on that guitar string then plucking it, yes that will change its resonant frequency. Without that finger on it, I think it makes the same note every time it's plucked.

Your reference to A on a keyboard at 440 Hz got me to thinking about a standard sporter weight 30 caliber 3.4 pound 24 inch barrel's resonant frequency. With both ends free its resonate frequency is at about 264 Hz.

Screw the breech end into a receiver bolted in a stock and its resonant frequency goes down to about 68 Hz. This is the one that causes the greatest angular swing of the muzzle axis.

If you smack that barrel with a hammer, it'll ring at a frequency much higher than these; couple thousand Hz for example.